Several methods for fabricating semiconductor devices utilize a plasma generated or maintained within a processing chamber. The character of the plasma within the chamber has an important effect upon the results of the fabrication process, such as etching or chemical vapor deposition.
For example, the quality of the plasma generated may be characterized by uniformity, plasma potential, and electron temperature among other characteristics. One kind of plasma reactor of interest is the inductively coupled plasma reactor. The plasma in such a reactor is generated inside a vacuum chamber by RF coils (also referred to as antenna), typically located on the top of the dome and/or around the outer side wall of the dome.
By adjusting the RF current in the coil, the density of the ions can be controlled. The energy of the ions can be controlled by another RF power, usually called RF bias, that is connected to the wafer pedestal. However, ion energy is not mono-energetic, and ion energy distribution is dependent on many factors, including but not limited to bias power and frequency, ion species, and plasma density.
One factor affecting the quality of the process on the wafer is fluctuation in dome temperature. Fluctuation in dome temperature may generate particles that deposit on the wafer and cause a lack of repeatability of a deposited film of material. In addition, variation in temperature over regions of the dome may result in excessive thermal stress that can ultimately result in dome fracture.
Another issue faced by the designers of plasma generation chambers is capacitive coupling between the RF coil and the ions of the plasma. Increased capacitive coupling between the coil and the plasma can give rise to an elevated plasma potential in the proximity of the dome surface, thereby increasing the energy of the ions impinging on the dome surface. High ion energies give rise to excessive ion bombardment on the dome wall adjacent to the RF coil, thereby increasing the number of contaminant particles and the temperature of the ceramic dome.
A number of techniques can be employed alone or in conjunction to reduce capacitive coupling. In one approach, a Faraday shield can be placed between the RF coils and the generated plasma. The Faraday shield is a grounded conductive layer that includes narrow, elongated openings having a major axis perpendicular to the windings of the RF coils. These openings allow magnetic flux entering the chamber to generate and sustain plasma, and act to suppress any eddy currents that would otherwise tend to be induced in the Faraday shield. The conductive and electrically grounded plane of the Faraday shield reduces capacitive coupling from high RF voltage in the coil to the plasma.
Given the importance of plasma-based processes to the fabrication of semiconductor devices, methods and structures permitting enhanced durability and reliability of plasma-based fabrication apparatuses are desirable.